Catalytic domain of the Serine/Threonine Kinase, Cell Division Cycle 2-like 1STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. CDC2L1, also called PITSLRE, exists in different isoforms which are named using the alias CDK11(p). The CDC2L1 gene produces two protein products, CDK11(p110) and CDK11(p58). CDC2L1 is also represented by the caspase-processed CDK11(p46). CDK11(p110), the major isoform, associates with cyclin L and is expressed throughout the cell cycle. It is involved in RNA processing and the regulation of transcription. CDK11(p58) associates with cyclin D3 and is expressed during the G2/M phase of the cell cycle. It plays roles in spindle morphogenesis, centrosome maturation, sister chromatid cohesion, and the completion of mitosis. CDK11(p46) is formed from the larger isoforms by caspases during TNFalpha- and Fas-induced apoptosis. It functions as a downstream effector kinase in apoptotic signaling pathways and interacts with eukaryotic initiation factor 3f (eIF3f), p21-activated kinase (PAK1), and Ran-binding protein (RanBPM). CDKs belong to a large family of STKs that are regulated by their cognate cyclins. Together, they are involved in the control of cell-cycle progression, transcription, and neuronal function. The CDC2L1 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.